Device and method for thermoforming an object having a back draft portion

ABSTRACT

The device for thermoforming an object ( 10 ) presenting an undercut portion ( 10 B) comprises: a thermoforming mold ( 12 ) having a base portion ( 13 ) and at least two undercut-forming portions ( 12 A,  12 B) in the vicinity of an end ( 12 ′); a countermold ( 18 ); and a moving thermoforming piston ( 20 ). The device further comprises holding means ( 23 A,  23 B) suitable for holding the rim ( 10 A) of the object ( 10 ) relative to the countermold ( 18 ), and, in order to unmold the object, said portions ( 12 A,  12 B,  13 ) of the mold ( 12 ) and the holding means ( 23 A,  23 B) are suitable for being controlled in a sequence in which the undercut-forming portions ( 12 A,  12 B) are moved apart, the holding means ( 23 A,  23 B) are active and hold the object ( 10 ) against the countermold ( 18 ), and at least the base portion ( 13 ) of the mold ( 12 ) is spaced apart from the countermold while the holding means are active. Translation of the title and the abstract as they were when originally filed by the Applicant. No account has been taken of any changes that may have been made subsequently by the PCT Authorities acting ex officio, e.g. under PCT Rules 37.2, 38.2, and/or 48.3.

The present invention relates to a device for thermoforming an objectpresenting an undercut portion and a base portion, the devicecomprising: a thermoforming mold having a base portion and at least twoundercut-forming portions in the vicinity of an open end; a countermoldhaving an end that is suitable for co-operating with said end of themold so as to clamp a piece of thermoplastic material thereagainst andso as to co-operate with said portions of the mold to define athermoforming cavity; and a thermoforming piston that is mounted to movebetween a thermoforming active position in which it penetrates into saidcavity and an inactive position in which it is situated outside saidcavity, the two undercut-forming portions of the mold being suitable forbeing moved apart so as to enable the object to be unmolded.

In the object that is to be thermoformed by a device of the invention,the undercut portion presents diametrical dimensions that are smallerthan the diametrical dimensions of the base portion. For example, theobject can be a bottle-shaped receptacle whose neck forms the undercutportion. It can also be a receptacle having a substantiallyfrustoconical side wall that tapers going towards the opening, or else areceptacle whose shape corresponds to the shape obtained from a spherecut along a plane parallel to its equator, which is then situatedbetween the resulting opening and the base of the receptacle.

When thermoforming objects that are free of undercuts, unmolding takesplace merely by moving the mold away from the opening in the object bymoving it in translation parallel to the movement of the thermoformingpiston. When thermoforming objects presenting undercuts, molding is morecomplicated and requires the use of a mold made up of a plurality ofportions.

Thus, FR 2 795 360 recommends using a mold having two undercut-formingportions and one base portion. For unmolding, firstly the twoundercut-forming portions are moved apart, and the thermoformed objectis held against the base portion of the mold by suction, said baseportion being provided with suction ducts. Said base portion can then bemoved to extract the object from the zone in which the undercut-formingportions of the mold are situated, in order to make it accessible bypick-up means that make it possible to transfer said object to theoutlet of the device.

That known device is relatively complicated because it implementsholding the object by suction against the base of the mold. Theeffectiveness of that suction must be excellent in order to enable theobject to be held correctly while the base portion of the mold is beingmoved.

In particular, in order to avoid the risks of the object tipping overrelative to said base portion, it is necessary for said base portion tocover the base portion of the object over a height that is sufficient.Once the base portion of the mold that is carrying the object has beenmoved far enough away from the undercut-forming portions of the mold, itis necessary to cause the suction to cease, and to separate the objectrelative to said base portion. This requires the object and the baseportion of the mold to be moved relative to each other parallel to thedirection in which the thermoforming piston is moved, in order toextract the base portion of the object from the base portion of themold, and then requires the object to be transferred sideways by movingit away from the thermoforming tool.

Thus, the way the various parts move relative to one another isrelatively complex, and, if it is assumed that the direction in whichthe thermoforming piston is displaced is vertical, the unmoldingoperation firstly requires the undercut-forming portions of the mold tobe moved horizontally so that they move away from the undercut portionof the object, it then requires the base portion of the mold to be movedvertically over a first stroke sufficient to move the rim of the objectaway from the undercut-forming portions of the mold, and said baseportion to be moved vertically or else the object to be moved verticallyrelative to said base station over a second stroke sufficient to unmoldthe base portion of the object relative to the base portion of the mold,and finally, it requires the object to be transferred horizontally. Inaddition, in general, the entire mold (including the undercut-formingportions must be capable of being moved over a small vertical stroke inorder to clamp the thermoplastic material between the mold an thecountermold.

FR 1 427 784 discloses another device in which, for unmolding an objectpresenting an undercut portion, firstly the undercut-forming portions ofthe mold are moved apart, and then the object is expelled from the baseportion of the mold by an ejector piston whose head forms the base ofthe mold during thermoforming. During that expulsion, the object ismerely carried by the head of the piston without being held relative toit, and there exists a risk that it might tip over or fall, therebygiving rise to wastage, or at least to reductions in manufacturingthroughputs. In addition, the device of FR 1 427 784 is possible onlywhen the mold and the countermold constitute respectively the bottomtool and the top tool of the thermoforming device. In other words, theobject must be thermoformed downwards.

FR 2 256 818 discloses yet another device in which, after thermoformingan object from a strip of thermoplastic, a front portion of the mold,which portion closes said mold on the downstream side in the directionof advance of the strip, is moved away so that the strip can advancethrough one step by extracting the object that has just beenthermoformed from the mold via the opening formed due to the front ofthe mold being opened. That device can be used only for thermoformingobjects from a continuous strip of thermoplastic material.

An object of the invention is to propose a device for thermoformingobjects presenting undercut portions that improves the above-mentionedprior art.

This object is achieved by the fact that the device further comprisesholding means suitable for holding the object relative to thecountermold, and by the fact that, in order to unmold the thermoformedobject, said portions of the mold and the holding means are suitable forbeing controlled in a sequence in which the undercut-forming portions ofthe mold are moved apart, said holding means are active and hold theobject relative to the countermold, and at least the base portion of themold is spaced apart from the countermold while the holding means areactive.

During the first stage of the sequence, in which stage theundercut-forming portions of the mold are moved apart, the object thathas just be thermoformed continues to be held between the countermoldand the base portion of the mold. Moving the undercut-forming portionsof the mold apart makes a portion of the wall of the object (e.g. a rimor a projecting portion on the object) accessible, and said object canthus be held relative to the countermold by holding means. In thissituation, the object can be totally unmolded by moving the base portionof the mold relative to the countermold. It can then be picked up bypick-up means so as to be removed from the thermoforming device, e.g. bybeing disposed in the next station, which is, for example, a fillingstation, of an installation including said device.

The way in which the various parts of the mold move during thermoformingis extremely simple and can be achieved rapidly. It is not necessary tomove the object relative to the countermold while it is being unmolded,and the object can be securely held against the countermold without anyof the risks of tipping that exist with the devices of FR 2 795 360 andFR 1 427 784. In particular, for unmolding, it is possible to move onlythe portions of the mold, without there being any need to move theobject that has just been thermoformed.

The invention applies both to a device in which the mold constitutes thebottom thermoforming tool and to a device in which the mold constitutesthe top tool. In addition, the device of the invention applies tothermoforming objects from distinct pieces of thermoplastic (one pieceper object), e.g. constituted by pellets of thermoplastic material.

Advantageously, the undercut-forming portions of the mold areconstrained to move with the base portion of the mold.

The various portions of the mold are then interconnected so that theundercut-forming portions can be moved apart without moving the baseportion of the mold, and so that finally moving the base portion inorder to move it away from the object held against the end of thecountermold makes it possible for complete unmolding to be achieved, thebase portion of the mold taking the undercut-forming portions away withit. This also facilitates the operation of closing the mold beforethermoforming another object because, for this purpose, the twoundercut-forming portions can be moved towards each other to define aclosed inside outline, a piece of thermoplastic material can be disposedon the end of the countermold or on the end of the mold, and said piececan be clamped between the countermold and the mold by moving the entiremold vertically towards the countermold.

Advantageously, the mold and the countermold are suitable for beingmoved relative to each other in order to place their respective ends outof contact before the two undercut-forming portions of the mold aremoved apart.

This movement can take place over a short stroke, e.g. of in theapproximate range a few tenths of a millimeter to 1 or 2 millimeters.This makes it possible to move the undercut-forming portions of the moldapart without them rubbing on the end of the countermold.

Advantageously, the holding means comprise holding members suitable forbeing moved between an active position in which they are suitable forholding the object relative to the countermold and an inactive position.

In one embodiment, for the purpose of unmolding the object, saidportions of the mold and the holding means are suitable for beingcontrolled in a sequence in which, in succession, the undercut-formingportions of the mold are moved apart, the holding means go from aninactive position to an active position in which they hold the objectrelative to the countermold, and the base portion of the mold is movedapart from the countermold.

In which case, the holding means are inactive during the thermoformingand go into their active position only after said thermoforming, e.g. bybeing moved in the join plane between the undercut-forming portions ofthe mold, which join plane is then open.

In another embodiment, the holding means are suitable for taking up aninactive position and an active position in which they define a portionof the wall of the thermoforming cavity and in which they are suitablefor holding the object relative to the countermold, and said holdingmeans are suitable for occupying their active position while the objectis being thermoformed, and while the undercut-forming portions of themold are being moved apart.

In which case, the holding means contribute to giving the wall of theobject its shape, and so long as they occupy their active position, theyhold the object securely by their shape being complementary to the shapeof the object.

The invention also provides a method of thermoforming an object havingan undercut portion and a base portion, the method consisting in: usinga thermoforming mold having a base portion and at least twoundercut-forming portions in the vicinity of an open end; clamping apiece of thermoplastic material by means of the end of a countermoldagainst said end of the mold; defining a thermoforming cavity with saidmold portions; bringing a thermoforming piston into a thermoformingactive position in which it penetrates into the cavity of the mold froman inactive position in which the piston is situated outside saidcavity; and, in order to enable the object to be unmolded, moving saidundercut-forming portions of the mold apart.

FR 2 795 360 describes a method in which, after the undercut-formingportions of the mold have been moved apart, the object that has justbeen thermoformed is held against the base portion of the mold bysuction, and said base portion is moved with the object that it carries.That holding is relatively unreliable and a risk exists that the objectmight tip over or fall while the base portion of the mold is beingmoved. In addition, that movement must be followed by an operation inwhich the object is unmolded relative to said base portion.

FR 1 427 784 discloses a method in which, after the undercut-formingportions have been moved apart, the object is expelled by means of anejector piston. As indicated above, such expulsion might also cause theobject to tip over or fall. In addition, that object can be thermoformeddownwards only.

FR 2 256 818 describes a method in which, after the front of the moldhas been opened, the strip of thermoplastic carrying the object that hasjust been thermoformed is caused to advance in order to unmold saidobject. Naturally, that method applies only to objects that arethermoformed from a continuous strip.

An object of the invention is to propose a method that improves themethods of the above-mentioned prior art.

This object is achieved by the fact that, for the purpose of unmoldingthe thermoformed object, it further consists in moving theundercut-forming portions of the mold apart, and in moving the baseportion of the mold away from the countermold while holding the objectrelative to the countermold.

Advantageously, while the object is being held relative to thecountermold, the undercut-forming portions and the base portion aremoved away from the countermold.

Advantageously, before the undercut-forming portions of the mold aremoved apart, the mold and the countermold are moved relative to eachother so as to place their respective ends out of contact.

Advantageously, in order to hold the object relative to the countermold,holding means are moved from an inactive position to an active position.

In one embodiment, this movement takes place after the undercut-formingportions of the mold have been moved apart.

In another embodiment, this movement takes place before the object isthermoformed, and said holding members are returned to their inactiveposition only once the undercut-forming portions of the mold have beenmoved apart.

In which case, advantageously, the object is thermoformed from a pelletof thermoplastic material, and, before said object is thermoformed, theperiphery of said pellet is shaped by means of the holding members.

The pellet reaches the thermoforming device after it has been heated andconveyed, which might have modified its shape. The shaping thusrectifies the periphery of the pellet prior to thermoforming. It isadvantageously performed by causing the holding members to go from theirinactive position to their active position, and it is advantageouslyaccompanied by or followed by die-stamping of the edge of the pellet.

The invention will be better understood and its advantages will appearmore clearly on reading the following detailed description ofembodiments given by way of non-limiting example. The description refersto the accompanying drawings, in which:

FIGS. 1, 3, and 5 are analogous vertical section views showing a firstembodiment of a device of the invention in three successive states,after an object has been thermoformed in the mold;

FIGS. 2, 4, and 6 are sections respectively on line II-II of FIG. 1, online IV-IV of FIG. 3, and on line VI-VI of FIG. 5;

FIG. 7 is an elevation view of a system using two devices of the firstembodiment of the invention;

FIG. 8 is a perspective view of the bottom portion of the system whichhas two thermoforming counter-tools;

FIG. 9 is a perspective view showing the top portion of this system thatincludes two thermoforming molds;

FIG. 10 is a fragmentary perspective view showing the bottom portion ofa device of a second embodiment of the invention; and

FIGS. 11, 12, and 13 are analogous fragmentary vertical section viewsdiagrammatically showing a device of the second embodiment of theinvention in three successive states before an object is thermoformed inthe mold.

The device shown in the figures serves to thermoform an object 10 which,in the example shown is in the form of a small bottle. The objectpresents a rim 10A, a neck undercut portion 10B and a base portion 10C.As indicated in the drawing, it can be seen that said object optionallyalso has an annular rib forming a collar 10D between the rim 10A and theneck 10B. Said collar can, for example, co-operate with atamper-proofing band on the cap of the receptacle.

The device includes a thermoforming mold 12 which has twoundercut-forming portions, respectively 12A and 12B, whose free endsdefine the open end 12′ of the mold. Said mold also includes a baseportion 13 which, in the example shown, is made up of a plurality ofpieces comprising a portion 13A whose inside periphery is cylindrical, abase portion proper 13B, a casing portion 13C disposed around said piece13B and secured thereto, and a ring 13D via which the portions 13C and13A are secured together.

In this example, the base portion 13B is cooled by means of a fluidcirculating in cooling ducts 14 with which it is provided.

In general, regardless of the number of pieces making up the mold, saidmold includes at least two undercut-forming portions and one baseportion.

The device also includes a countermold 18 that has one end 18′ suitablefor co-operating with the end 12′ of the mold to clamp a piece ofthermoplastic material thereagainst, and a thermoforming piston 20mounted to move between a thermoforming active position (not shown) inwhich it penetrates into the cavity 16 and an inactive position (asshown) in which it is outside said cavity.

The various portions of the mold, as considered together with thecountermold 18, define a thermoforming mold 16.

In the example shown, the object is thermoformed upwards, i.e. thecountermold and the mold respectively form the bottom thermoforming tooland the top thermoforming tool. The reverse configuration could be usedfor thermoforming the object 10 downwards.

The device also includes two hinged arms 22A and 22B that are hinged tothe countermold.

The device includes holding means that comprise fingers movable in thejoin plane in which the undercut-forming portions of the mold join. Inthe example shown, said fingers are formed by the ends 23A and 23B ofthe hinged arms 22A and 22B. By examining FIG. 8, it can be understoodthat the wall of the countermold 18 is provided with recesses 24enabling said hinged arms to be mounted to pivot about their hinge pins26. Said pins extend perpendicularly to the direction D in which thethermoforming piston moves.

In FIGS. 1 and 8, the holding means constituted by the fingers 23A and23B are in their inactive position in which they are spaced apart fromthe end 12′ of the countermold. The fingers 23A and 23B are thenreceived in part in setbacks 28 (FIG. 1), each of which is provided inpart in each of the two undercut-forming portions 12A and 12B, in thevicinity of the end 12′ of the mold.

As can be understood by examining, for example, FIGS. 2 and 9, theundercut-forming portions 12A and 12B carry cooling plates, respectively12′A and 12′B, which are provided with bores 11 through which thecooling fluid, e.g. air, can flow. It is between said cooling platesthat the above-mentioned setbacks 28 are provided.

In dashed lines, FIG. 2 shows the join plane 12″ between theundercut-forming portions 12A and 13B of the mold, and also the setback28 in which the finger 23A is disposed.

In FIGS. 1 and 2, the mold is closed, i.e. the undercut-forming portions12A and 12B are closed against each other in their join plane, and theirinside peripheries co-operate with the inside periphery of the baseportion and with the end 18′ of the countermold to define theabove-mentioned cavity 16. In this situation, a piece of thermoplasticmaterial such as a pellet can be clamped between the facing edges of themold and of the countermold, before being deformed by the thermoformingpiston so as to be brought into the cavity 16. It is pressed against thewall of the cavity by blowing air through the orifice 29 situated in thecountermold 18.

Naturally, prior to being deposited between the mold and thecountermold, the pellet of thermoplastic material is subjected to aheating step inside a heater box and to a transfer step for transferringit from the heating station to the thermoforming device. Any heater andtransfer means can be devised for disposing the hot pellet between themold and the countermold. In particular, inspiration can be taken fromthe means disclosed by FR 2 766 123 and by FR 01 11031 (not yetpublished on the date of filing of the present patent application).

In FIGS. 1 and 2, the receptacle 10 has just been thermoformed, and thepiston 20 has just been returned to its low position, inside thecountermold. The receptacle 10 must then be unmolded.

Unmolding takes place by moving the various portions of the moldrelative to each other in a sequence whose successive stages are shownby FIGS. 3 and 4 firstly, and by FIGS. 5 and 6, secondly.

FIG. 4 shows that the two undercut-forming portions 12A and 12B havebeen moved apart. Making advantageous use of the resulting gap, it hasbeen possible for holding means to be activated, and it can be seen inFIG. 3 that the arms 22A and 22B have pivoted about their respectivepins 26 so that their ends forming the fingers 23A and 23B are situatedabove the end 18′ of the countermold. The holding means are thusactivated by moving into the gap opened up between the undercut-formingportions 12A and 12B due to them being moved apart. In this position,the fingers 23A and 23B hold the rim 10A of the receptacle 10 againstthe end 18′ of the countermold. During this stage in which theundercut-forming portions 12A and 12B are moved apart and the holdingmeans 23A and 23B are driven, the receptacle 10A continues to be heldcorrectly because the base portion 10C of the mold has not movedsignificantly. There is therefore no risk of the receptacle 10 tippingover or falling. As soon as the portions 12A and 12B have been movedapart sufficiently, it is possible to control the arms so that they cometo hold the rim of the receptacle against the end of the countermold.

It is then possible to implement the next stage of the sequence, shownin FIGS. 5 and 6. This stage consists in moving at least the baseportion 13 of the mold so as to unmold the receptacle 10 while holdingsaid receptacle by means of the fingers 23A and 23B which continue toclamp the rim 10A of the receptacle against the end 18′ of thecountermold.

In this example, it is with the rim 10A of the receptacle 10 that theholding fingers co-operate. When such a rim exists, said rim constitutesa projecting portion that can easily be retained by the fingers.However, they can also be engaged behind the collar 10D.

This system can also apply to objects without rims or withoutsignificantly projecting portions, e.g. by increasing the area ofcontact between the ends of the holding fingers and the wall of theobject, it being possible for said ends to be provided with concaveshapes adapted to match the outline of the object. It is also possibleto imagine making provision for the fingers, in their active position,to deform the wall of the object elastically in order to hold it moresecurely.

In a first possible variant, during this last stage of the unmolding,only the base portion 13 of the mold is moved in the direction D inwhich the thermoforming piston is moved so as to move it away from thecountermold, while the undercut-forming portions are merely moved apartsufficiently by being moved in relative translation perpendicularly tosaid direction D in order to enable the receptacle then to be picked upby the pick-up means such as a grab 30 and to be moved away from thethermoforming tool by being carried by said pick-up means.

In an advantageous variant shown in the drawings, the undercut-formingportions 12A and 12B of the mold are constrained to move with the baseportion 13.

In which case, during the first stage, the two undercut-forming portions12A and 12B are merely moved apart so as to define between them minimumdiametrical dimensions D1 that are at least equal to the maximumexternal diametrical dimensions D2 of the receptacle 10, also defined bythe dimensions of the cavity 16. Under such conditions, in order toachieve the unmolding, it suffices to move the entire mold in thedirection D over a distance sufficient for the end 12′ of the mold to bespaced apart from the end 18′ of the countermold by a distance greaterthan the total height H of the receptacle, as shown in FIGS. 5 and 6. Inthis situation, since the receptacle is still held against the end ofthe countermold by the fingers 23A and 23B, it suffices to pick it upusing pick-up means such as the arms 30A and 30B of a grab 30, e.g. ofthe type shown diagrammatically in FR 2 766 123 and, only then, to causethe holding fingers to return to their inactive position in which theyare spaced apart from the end of the countermold, in order to move thepick-up means holding the receptacle 10 so as to remove said receptaclefrom the thermoforming device by placing it, for example, in a fillingstation of an thermoforming and filling installation.

Thus, the pick-up means 30A and 30B and the holding means 23A, 23B areadapted to be controlled such that the pick-up means 30A, 30B pick upthe receptacle 10 while the holding means 23A, 23B hold said receptacleagainst the end 18′ of the countermold 18, then the holding means 23A,23B cease to hold the receptacle and the pick-up means 30A, 30B aremoved to bring said receptacle outside the thermoforming device.

Advantageously, the mold 12 and the countermold 18 are suitable forbeing moved relative to each other so as to place their respective ends12′ and 18′ out of contact before the two undercut-forming portions 12Aand 12B are moved apart. This variant is not shown, but it can beunderstood, by examining FIG. 2, that it suffices to move the mold andthe countermold relative to each other in the direction D so as to movetheir respective ends apart by a small distance e, e.g. of about a fewtenths of a millimeter, without yet performing the unmolding, beforemoving the undercut-forming portions of the mold relative to each otheras shown in FIGS. 3 and 4.

FIG. 7 shows a thermoforming system using two devices of theabove-described type, it naturally being understood that a differentnumber of devices (one or more than two) could be used in the samesystem. In FIG. 7, the left device is given the references used in FIGS.1 to 6, while the right device is given the same references plus 100.

The two countermolds 18 and 118 are carried by the same bottom supportplate 40, while the two molds 12 and 112 are carried by a common topsupport plate 42. It should be recalled that the configuration of themolds and countermolds could be reversed, it being possible for themolds to be situated under the countermolds.

The plates 40 and 42 are mounted to move relative to each other whilebeing guided by guide columns 44. By means of actuators (not shown),they can be moved apart so as to move the molds and countermoldsrelative to one another in the direction D. By examining FIGS. 7 and 8,it can be seen that the pivot pin 26 of the arms 22A and 122A extends inthe space provided between the two blocks of countermolds 18 and 118,and that an actuator 46 co-operates with said pin to cause the arms 22Aand 122A to pivot simultaneously. Said actuator 46 also co-operates withthe pin 26 that interconnects the arms 22B and 122B between the twoblocks of countermolds so as also to cause them to pivot simultaneously.Thus, controlling the actuator 46 simultaneously places the holdingmeans of the two countermolds in their respective active positions orelse in their respective inactive positions.

FIG. 8 shows said holding means in their inactive position. FIG. 8 alsoshows that each of the ends 18′ and 118′ of the countermolds 18 and 118carries a shaping clamp, respectively 48 and 148, each of which has twoarms, respectively 48A & 48B and 148A & 148B. When the mold is separatedfrom the countermold, the arms of said clamps are moved apart so as toopen up a relatively wide opening at the end of the countermold. Apellet of thermoplastic material, even if it is slightly deformed afterit has been heated in the heater box, can thus be disposed at the end ofthe countermold by being laid on the die-stamping ledge respectively 50and 150 formed at the end of the countermold, respectively 18′ and 118′,inside the opening opened up between the arms of the shaping clamp. Saidarms are mounted to pivot relative to each other about a pin 49, 149that is parallel to the direction D in which the thermoforming pistonmoves. Said pin 49 can also be seen in FIGS. 1, 3, and 5.

The end of each of the arms 48A and 48B that is opposite from their pin49 carries a wheel, respectively 51A and 51B. Similarly, the end of eachof the arms 148A and 148 carries a wheel, respectively 151A and 151B.The end of the mold 12 carries fingers, respectively 53A and 53B (seeFIG. 7) which, while the mold 12 and the countermold 18 are beingbrought towards each other for the purpose of clamping between them thepellet of thermoplastic material, co-operate, via ramps with which theyare provided, with the wheels 51A and 51B to close the clamp 48 bymoving its two arms towards each other. Similarly, the end of the mold112 carries analogous fingers 153A, 153B suitable for co-operating withthe wheels 151A and 151B.

As described in Patent Application FR 01 11031, the ends of the mold andof the countermold can form die-stamping means for the edges of thepellet of thermoplastic material.

The extent to which the arms of the clamp 48 can open can be limited byabutment means, respectively 53A and 53B formed by stationary lugspenetrating into windows provided in the arms. In addition, said armsare urged continuously back towards their spaced-apart position byresilient means (not shown). The clamp 48 can be mounted on springs 55(see FIGS. 2, 4, and 6) which urge it continuously back into its highposition shown in FIG. 8, in which the thickness of a pellet can bereceived in the thickness of the arms 48A and 48B, which springs extendbeyond the die-stamping edge 50 and can be compressed while the mold isclosed against the countermold so as to bring the top face of the clampsubstantially into the same plane as the top end 18′ of the countermold,as can be seen in FIGS. 1 to 6.

With reference to FIGS. 7 to 9, the top portion of the thermoformingsystem that comprises the molds of the two thermoforming devices isdescribed in more detail below. It can be seen that the system includeslinks, respectively 58A and 58B which are interconnected via a commontube 60 whose two ends co-operate with respective ones of oblong slots,such as the slot 59A, provided in each of the two links. The tube 60 ismoved by an actuator 62 that can also be seen in FIGS. 1, 3, and 5. Atits end opposite from the slot that co-operates with one end of the tube60, each link carries a vertical pin, respectively 62A and 62B which isdriven in rotation by the link moving so as also to drive in rotation aneccentric such as the eccentric 64A that can be seen in FIGS. 7 and 9.This eccentric is provided with a lug that co-operates with a slot,respectively 66A and 66B, formed in a slat, respectively 68A and 68B.The slat 68A carries two horizontal displacement bars, respectively 70Aand 70′A, and the slat 68B also carries two horizontal displacementbars, respectively 70B and 70′B. The bars 70A and 70′A pass through theundercut-forming portions 12A, 12B, and 112A, the undercut-formingportions 12A and 112A being constrained to move with bars 70A and 70′A,while said bars are mounted to slide freely relative to the portion 12B.Similarly, the bars 70B and 70′B pass through the undercut-formingportions 112B, 112A and 12B, the portions 112B and 12B being constrainedto move with the bars 70B and 70′B, while said bars are mounted to slidefreely in the portions 112A.

FIGS. 7 and 9 show the configuration in which the undercut-formingportions 12A & 12B and 112A & 112B are closed against one anotherrespectively. When the actuator 62 is operated, the rod 60 can be movedin the direction T indicated in FIGS. 7 and 9, thereby pivoting theeccentrics driven by the pins 62A and 62B in the slots 66A and 66B, andmoving the slats 68A and 68B correspondingly. Since the dispositions ofthe eccentrics in their respective slots 66A and 66B are reversed, themovement causes the slats 68A and 68B to be moved apart by moving themrespectively in the direction T1 and in the direction T2 (which, in thisexample, is identical to the direction T). As a result, theundercut-forming portions 12A and 12B are moved apart, and theundercut-forming portions 112A and 112B are also moved apart. Bars 70A,70B, 70′A, 70′B are carried by a support portion, respectively 72A and72B, which is itself carried by the support plate 42. Thus, theundercut-forming portions of the molds are constrained to movevertically with the base portions 13 and 113 of the molds.

A second embodiment of the invention is described below with referenceto FIGS. 10 to 13.

FIG. 10 shows the top portion of a countermold 218 that carries holdingmembers 223A, 223B, and 223C. Said holding members present edgeportions, respectively 223′A, 223′B and 223′C which, when the holdingmembers shown in FIG. 10 are in the active position, define a closedoutline at the end of the countermold. As can be seen in FIGS. 11 to 13,a pellet of thermoplastic material 201 disposed on the end 218′ of thecountermold 218 can be wedged in said closed outline for the purpose offorming an object such as the receptacle 10 of the preceding figures.The holding members are constituted by tabs or fingers that can bedisplaced radially relative to the axis A of the countermold 218, saidaxis being parallel to the direction D in which the thermoforming pistonis moved. For this purpose, a cam-carrying ring 260 disposed at the endof the countermold 218 can be driven in rotation by an actuator of whichonly the head 261 is shown. Said ring is provided with slots 262 formingcams in which wheels 264 are disposed, each wheel being secured to arespective holding member 223A, 223B, or 223C. The slots 262 formeccentric portions with which said wheels co-operate, and it can beunderstood that, by turning the ring 260 in the direction R1, it ispossible to cause the edges of the holding members to be moved away fromthe axis A so as to bring said members into their inactive position,whereas rotating the ring in the opposite direction causes the edges ofthe holding member to be moved towards each other so as to bring theminto their active position shown in FIG. 10.

Between the two positions, the holding members move radially by beingguided by guide means such as, for each guide member, a rectilinear rib266 having an upside-down T-shaped section, for example, and beingmounted to slide in a groove 268 which has a complementary section andwhich is formed in a central plate 270 above which the holding membersare disposed. Said plate is substantially in the shape of a ring thatsurrounds the top end portion of the countermold inside which thethermoforming piston moves.

The plate 270 also makes it possible to guide the ring 260 as it turns.For this purpose, the outside periphery of said plate is provided withan annular rib 272 or with a plurality of segments of annular rib while,over its inside periphery that co-operates with said outside periphery,the ring 260 is provided with an annular groove 274 disposed around therib 272.

As indicated diagrammatically in FIGS. 11 to 13, the plate 270 and thering 260 that is carried by said plate, as well as the holding members223A, 223B, and 223C, are supported relative to the body of thecountermold by springs 271. The holding members are thus supportedresiliently relative to the countermold between a wedging position whichcan be seen in FIG. 11 and in FIG. 12, and in which, with the mold beingspaced apart from the countermold, said members project beyond the endof the countermold over a given projection distance DE, and a retractedposition shown in FIG. 13 and in which said projection distance isreduced, optionally to zero.

In this example, in the retracted position shown in FIG. 13, theprojection distance is reduced to a distance DF that is less than thedistance DE without being zero.

Each of the edge portions 233′A, 223′B, and 223′C is provided with atleast one piece in relief for anchoring into the thermoplastic materialand, in the retraction position shown in FIG. 13, said piece in reliefis situated in a region of the holding members that continues to projectbeyond the top end 218′ of the countermold. Said piece in relief can beconstituted by a recess or by a projection. In this example, it is anannular groove 224 that is made up of a plurality of groove portions,each of which is provided in the edge portion of a respective holdingmember. When, with the holding members in their active position, saidedge portions define a closed outline, said groove portions togetherform a continuous groove 224.

Rather than providing a continuous groove, it is possible to provide aplurality of recessed portions in the edges of the holding membersforming a plurality of recessed anchoring pieces in relief. It is alsonaturally possible to provide a plurality of projecting ribs or ribportions disposed so as to form a continuous annular rib when theholding members are in their active position.

Initially, with the holding members being in their inactive positionwhich can be seen in FIG. 11, and into which each of them is movedrelative to the active position shown in FIG. 10 by moving away from theaxis, they define, as considered together, an opening of diametergreater than the diameter of the top end of the countermold.

Then as indicated by the arrows of FIG. 12, the holding members arebrought into their active position so that their respective edgeportions co-operate with the edge of the pellet 201. The closed outlinedefined by the edge portions of the holding members when they are intheir active position corresponds to the outline of a portion of thereceptacle that is to be thermoformed and, if the pellet has beenslightly deformed, this step in which the holding members are movedtowards their active position makes it possible to shape the peripheryof the pellet in a manner such as to impart the desired shape to it.

At this stage, since the mold is still spaced apart from the countermoldor, at least, is not exerting any pressure thereon, the holding membersare still in their wedging position. As can be seen in FIG. 13, it isthen possible to move the mold towards the countermold in order to clampthe pellet 201 between the facing ends of the countermold and of themold. In moving in this way, the mold exerts a pressure on the holdingmembers, thereby bringing them into their retracted position shown inFIG. 13. Naturally, this movement also affects the ring 260 and theplate 270.

Since the material of the pellet 201 is hot, it can then be deformedplastically and tends to fill the groove 224. This phenomenon also makesit possible to perform die-stamping on the edge of the pellet, therebygiving the edge portion of the thermoformed object its shape. In thissituation, thermoforming is then performed conventionally by moving thethermoforming piston inside the cavity of the mold.

When the thermoforming operation is finished, the thermoformed objectmust be unmolded. For this purpose, as indicated above, and inaccordance with the invention, the undercut-forming portions 12A and 12Bof the mold are moved apart without moving the base portion of saidmold. In this situation, the object that has just been thermoformedremains securely held due to the presence of the rib of thermoplasticmaterial that has formed inside the groove 224. This opposes anyuntimely tearing away or tipping over of the object relative to thecountermold.

Advantageously, before moving the undercut-forming portions of the moldrelative to each other in this way, said mold is raised slightly so asto cause the pressure exerted by the mold on the countermoldsubstantially to cease. Due to the presence of the above-mentionedsprings 271, the holding members and the ring 260 and the plate 270 arethen lifted slightly relative to the body of the countermold. Thereceptacle that has just been thermoformed thus moves slightly away fromthe end 218′ of the countermold, but it remains securely held inside theclosed outline defined by the edge portions of the holding members.

As indicated above, it is possible, by way of anchoring relief forfacilitating holding of the thermoformed object by the holding means, toprovide one or more projections formed on the edge portions of theholding means. In which case, when the holding members are brought intotheir active position as shown in FIG. 12, said projections tend tocatch in the edge of the pellet of thermoplastic material. Then, whenthe mold is moved towards the countermold to reach the situation shownin FIG. 13, the projecting pieces in relief move relative to the pelletwhich fills the space defined between the facing ends of the mold and ofthe countermold.

In the second embodiment of the invention, the holding members are intheir active position during the thermoforming and it can be understoodfrom FIG. 13 that they then define a portion of the wall of thethermoforming cavity. More precisely, a portion of said cavity that issituated between the facing ends of the mold and of the countermold isdefined by that fraction of the edge portions of the holding memberswhich projects by the distance DF beyond the end 218′ of thecountermold.

In the second embodiment, the mold can be identical to the molddescribed with reference to the preceding figures, in particular-withreference to FIG. 9.

In the first embodiment, it is possible to replace the holding fingers22A and 22B with suitable shaping of the edge portions of the shapingclamps 48A and 48B which then perform the same role as the holdingmembers 223A, 223B, and 223C of the second embodiment. However, it isthen necessary to modify the mode of actuating the arms of said clamps,e.g. by using an actuator that moves them towards each other or thatmoves them apart independently of the movement of the mold, so that saidarms remain closed while the undercut-forming portions of the mold aremoving relative to each other so as to continue to hold the objectduring this movement.

In the second embodiment, the anchoring pieces in relief generateimprints in the wall of the thermoformed object. Said imprints can beformed in the rim or else be situated thereunder.

The anchoring pieces in relief can also contribute to forming a specificportion of said object, e.g. a S portion of the fastening collar forfastening to a tamper-proofing band for a cap.

1. A device for thermoforming an object presenting an undercut portionand a base portion, the device comprising: a thermoforming mold having abase portion and at least two undercut-forming portions in the vicinityof an open end; a countermold having an end that is suitable forco-operating with said end of the mold so as to clamp a piece ofthermoplastic material thereagainst and so as to co-operate with saidportions of the mold to define a thermoforming cavity; and athermoforming piston that is mounted to move between a thermoformingactive position in which said piston penetrates into said cavity and aninactive position in which said piston is situated outside said cavity,the two undercut-forming portions of the mold being suitable for beingmoved apart so as to enable the object to be unmolded; the devicefurther comprising holding means suitable for holding the objectrelative to the countermold and, in order to unmold the thermoformedobject, said portions of the mold and the holding means being suitablefor being controlled in a sequence in which the undercut-formingportions of the mold are moved apart, said holding means are active andhold the object relative to the countermold, and at least the baseportion of the mold is spaced apart from the countermold while theholding means are active.
 2. A device according to claim 1, wherein theundercut-forming portions of the mold are constrained to move with thebase portion of the mold.
 3. A device according to claim 1, wherein themold and the countermold are suitable for being moved relative to eachother in order to place respective ends thereof out of contact beforethe two undercut-forming portions of the mold are moved apart.
 4. Adevice according to claim 1, further comprising pick-up means suitablefor picking up the object after said object has been unmolded, saidpick-up means and the holding means being suitable for being controlledsuch that the pick-up means pick up the object while the holding meansare holding said object against the end of the countermold then theholding means cease to hold the object and the pick-up means are movedto bring the object out of the thermoforming device.
 5. A deviceaccording to claim 1, wherein the holding means comprise holding memberssuitable for being moved between an active position in which saidmembers are suitable for holding the object relative to the countermoldand an inactive position.
 6. A device according to claim 5, wherein theholding means comprise fingers secured to arms that are hinged to thecountermold.
 7. A device according to claims 1, wherein the holdingmeans comprise fingers integral with arms that are hinged to thecountermold.
 8. A device according to claim 1, wherein, for the purposeof unmolding the object, said portions of the mold and the holding meansare suitable for being controlled in a sequence in which, in succession,the undercut-forming portions of the mold are moved apart, the holdingmeans go from an inactive position to an active position in which saidholding means hold the object relative to the countermold, and the baseportion of the mold is moved apart from the countermold.
 9. A deviceaccording to claim 8, wherein the holding means comprise fingers whichare mounted to move in a join plane in which the undercut-formingportions of the mold join.
 10. A device according to claim 1, whereinthe holding means are suitable for taking up an inactive position and anactive position in which said holding means define a portion of the wallof the thermoforming cavity and in which said holding means are suitablefor holding the object relative to the countermold, and wherein saidholding means are suitable for occupying the active position thereofwhile the object is being thermoformed, and while the undercut-formingportions of the mold are being moved apart.
 11. A device according toclaim 10, wherein the holding means comprise holding members suitablefor being moved between an active position in which said members aresuitable for holding the object relative to the countermold and aninactive position and wherein the holding members present edge portionswhich, when said members are in the active position, define, at the endof the countermold, a closed outline in which a pellet of thermoplasticmaterial disposed on the end of the countermold can be wedged for thepurpose of being thermoformed in order to form said object.
 12. A deviceaccording to claim 11, wherein the holding members are supportedresiliently relative to the countermold between a wedging position inwhich, with the mold being spaced apart from the countermold, saidmembers project beyond the end of the countermold over a givenprojection distance, and a retracted position in which said projectiondistance is a distance that is reduced or optionally zero. 13.(canceled)
 14. (canceled)
 15. A method according to claim 24, wherein,while the object is being held relative to the countermold, theundercut-forming portions and the base portion are moved away from thecountermold.
 16. A method according to claim 24, wherein, before theundercut-forming portions of the mold are moved apart, the mold and thecountermold are moved relative to each other so as to place theirrespective ends out of contact.
 17. A method according to claim 24,wherein, after unmolding the object is picked up by pick-up means, saidobject ceases to be held relative to the countermold, and the pick-upmeans carrying the object are moved.
 18. A method according to claim 24,wherein, in order to hold the object relative to the countermold,holding means are moved from an inactive position to an active positionin which said holding means are suitable for holding the object relativeto the countermold.
 19. A method according to claim 18, wherein theholding means are moved from their inactive position to the activeposition after the undercut-forming portions of the mold have been movedapart from each other.
 20. A method according to claim 24, wherein, inorder to hold the object relative to the countermold, the holdingmembers are moved between the undercut-forming portions of the mold, asspaced apart from each other.
 21. A method according to claim 18,wherein the holding members are moved from the inactive position thereofto the active position before the object is thermoformed, and whereinsaid holding members are returned to their inactive position only oncethe undercut-forming portions of the mold have been moved apart.
 22. Amethod according to claim 21, wherein the object is thermoformed from apellet of thermoplastic material, and wherein, before said object isthermoformed, the periphery of said pellet is shaped by means of theholding members.
 23. A device according to claim 11, wherein each of theedge portions is provided with at least one anchoring piece in relieffor anchoring into the thermoplastic material.
 24. A method ofthermoforming an object presenting an undercut portion and a baseportion, the method comprising the steps of in: using a thermoformingmold having a base portion and at least two undercut-forming portions inthe vicinity of an open end; clamping a piece of thermoplastic materialby means of the end of a countermold against said end of the mold;defining a thermoforming cavity with said mold portions; bringing athermoforming piston into a thermoforming active position in which saidpiston penetrates into the cavity of the mold from an inactive positionin which the piston is situated outside said cavity; and, in order toenable the object to be unmolded, moving said undercut-forming portionsof the mold apart; and moving the base portion of the mold away from thecountermold while holding the object relative to the countermold.